The present invention relates to washing machines of the drum type having a drum which is rotatable with the center of rotation thereof positioned horizontally or as inclined.
FIG. 10 shows a drum-type washing machine 90 which comprises a drum 91 rotatable in a horizontal or inclined state for washing laundry and dewatering therefrom. The drum 91 is disposed in and rotatably supported by an outer tub 92, coupled to a drive motor 93 on the outer tub 92 by a belt 94 and pulleys 95, 95 and rotated by the motor 93.
Especially when water is removed, the wet laundry in the washing machine 90 is positioned eccentrically on the inner peripheral wall of the drum 91 by a centrifugal action, with the result than an unbalanced load occurs on the drum 91, producing imbalance under gravity around the center of rotation and giving rise to the problem of vibration or noise.
To prevent the vibration from being transmitted to the outside, vibration reducing dampers 97 and springs 97a are arranged between the outer tub 92 supporting the drum 91 and the machine cabinet 96.
In order to prevent the occurrence of an eccentric load to diminish vibration and noise, some washing machines have a plurality of liquid holding chambers 98 provided at a drum end and equidistantly arranged in the same direction, and means 99 for detecting the position of eccentricity of the load. The amounts of liquid in the liquid holding chambers 98 are adjusted in accordance with the position of eccentric load detected by the eccentric load detecting means 99 to offset the eccentric load of the drum 91 and reduce the vibration and noise.
Washing machines are conventionally available wherein the outer tub 92 is provided with an acceleration sensor serving as the eccentric load detecting means 99 and adapted to detect the acceleration in the upward or downward direction of the outer tub 92 to specifically determine the position of eccentric load.
The amounts of liquid in the liquid holding chambers 98 are adjusted by supplying approximately uniform amounts of water to the chambers 98 in advance, and momentarily reversely rotating the drive motor 93 upon the position of eccentric load reaching approximately a position exactly above the center of rotation of the drum 91 to brake the motor by the reverse rotation and allow the water to spontaneously fall from the chambers 98 on the side of eccentric load.
However, since the magnitude of braking force remains the same regardless of the weight of the laundry, the brake is less effective when the weight of the laundry is great, and the amounts of water in the chambers 98 not located at the position of the eccentric load diminish. For this reason, the balance of eccentric weight under gravity remains uncorrected despite the adjustment of amounts of water in the chambers 98, augmenting the vibration of the drum 91.
An object of the present invention is to provide a drum-type washing machine wherein the magnitude of braking force is altered in accordance with the weight of laundry in the drum by detecting the moment of inertia of the drum so as to make it possible to correctly adjust the amounts of liquid in liquid holding chambers.
To fulfill the above object, the present invention provides a washing machine of the drum type comprising:
a drum rotatable about a horizontal or inclined center of rotation with laundry placed therein for washing the laundry and dewatering therefrom,
a drive motor for rotating the drum,
a plurality of liquid holding chambers arranged circumferentially of the drum at equal intervals for holding a liquid therein by a centrifugal force produced by the rotation of the drum,
means for detecting an eccentric load due to uneven presence of the laundry within the drum, and
control means for determining the position and magnitude of the eccentric load detected and adjusting the amounts of liquid in the liquid holding chambers in accordance with the position and magnitude of the eccentric load,
the amounts of liquid in the liquid holding chambers being adjustable by braking the drum in rotation.
The washing machine has moment of inertia measuring means for detecting the rotation of the drum. The control means calculates the moment of inertia acting on the drum based on the rotation of the drum detected by the moment of inertia measuring means, and adjusts the magnitude of braking force to be applied to the drum in accordance with the calculated moment of inertia so as to decelerate the drum at a constant rate in adjusting the amounts of liquid in the liquid holding chambers.
The moment of inertia detecting means detects the rotation of the drum having laundry placed therein, for example, the speed of rotation or the number of revolutions of the drum, and the control means calculates the moment of inertia from the data obtained. The moment of inertia of the drum varies with the weight of the laundry, so that in adjusting the amount of liquid in the liquid holding chambers, if the magnitude of braking force is so adjusted as to decelerate the drum at a constant rate based on the moment of inertia of the drum, the drum can be decelerated at the same position irrespective of the weight of the laundry, and the amount of liquid in the chambers is adjustable in accordance with the position of eccentric load.
The changes of polarity of the magnetic poles of the drive motor are detected as moment of inertia measuring means to detect the rotation of the drum from the rotation of the drive motor, so that the moment of inertia can be measured also accurately. The braking force is adjusted based on the information as to the moment of inertia as accurately determined, whereby the amounts of liquid in the liquid holding chambers can be adjusted accurately to assure the drum of weight balance and result in diminished vibration and lower noise.
Hall elements which are generally provided on drive motors can be utilized as the magnetic pole detecting means. This serves to reduce the increase in the number of parts and to suppress the cost increase.
When a direct drive motor is used as the drive motor so as to connect the drum directly to the rotation shaft of the drive motor without using any reduction gear, no slippage occurs between the drum and the drive motor. The rotation of the drive motor is then in match with that of the drum, permitting the measurement of the moment of inertia with higher accuracy.